I was going to use it to convert from an MPEG TS to LXF and vice-versa. It would only really be 708 captioning data, maybe even AFD data in the packets as well.

Even if the VBI 708 captioning packets could be outputted to a captioning file separate from the video/audio would be beneficial. VLC can decode 708 captioning from VBI data when in an MPEG TS so there is an open source implementation of VBI data decoding.

I can provide some TS and LXF samples of video with VBI data if needed.